The present disclosure relates to a coordinate measuring machine and, more particularly, to an arm of a portable articulated coordinate measuring machine.
Portable articulated arm coordinate measuring machines (AACMMs) have found widespread use in the manufacturing or production of parts where there is a need to rapidly and accurately verify the dimensions of the part during various stages of the manufacturing (e.g. machining) or production of the part. Portable AACMMs represent a vast improvement over known stationary or fixed, cost-intensive, and relatively difficult to use measurement installations, particularly in the amount of time it takes to perform dimensional measurements of relatively complex parts. Typically a user of a portable AACMM simply guides a probe along the surface of the part or object to be measured. The measurement data are then recorded and provided to the user. In some cases, the data are provided to the user in visual form, for example, three dimensional (3-D) form on a computer screen. Alternatively, the data may be provided to the user in numeric form, for example, when measuring the diameter of a hole, the text “Diameter=” is displayed on a computer screen.
Arm portions of AACMMs may be susceptible to twist due to temperature changes. Twisting of a portion of an arm segment may cause a coupled encoder to rotate, thereby generating an angle error and reducing the accuracy of the machine. Such a twisting may be caused for example by a patterned composite material on an outer region of the arm segment, the outer region having a non-uniform pattern. In general, such twisting effects cannot be removed by measuring temperatures, especially since temperature sensors are ordinarily located in the interior of the arm segments. A method is needed to minimize twisting of the arm segments.